Post on 18-Sep-2018
Current Literature Jingbo Xiao June 5th, 2004
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Stereospecific and Stereodivergent Construction ofQuaternary Carbon Centers through Switchable
Directed/Nondirected Allylic Substitution
Bernhard Breit*, Peter Demel, Christopher Studte
Institut für Organische Chemie und Biochemie Albert-Ludwigs-UniversitätFreiburg, Germany
Angewandte Chemie International Edition,2004 Early View Communication
Current Literature Jingbo Xiao June 5th, 2004
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Quaternary Carbon Centers1. Ionic constructions which may involve the participation of the tertiary carbon atom as a
nucleophilic or as an electrophilic reaction partner
NH
NO
NH
NO1. LDA (2 eq.)
2. BrCH2CO2Me
CO2Me Cl (n-BuC )3Al+
71% n-Bu
2. Oxidative and reductive coupling reactions
HO
OH
VOCl375%
HO
O
3. Rearrangement reactions
R1 OHR2X R4
R3-X- R1 O
R2R3 R4 O
O
2300CO
O
4. Cycloaddition reactionsTetrahedron, 1980, 36, 419
Current Literature Jingbo Xiao June 5th, 2004
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Asymmetric Creation of Quaternary Carbon Centers
1. Enantioselective Creation (one chiral center was generated in product)
A. Enantiodifferentiating Reactions (0 to 1)1. Chemical Methods2. Biological Methods
B. Diastereodifferentiating Reactions (2 to 1)1. Use of Chiral Nucleofuges2. Intramolecular Chiral transfer Reactions3. Miscellaneous Reactions
2. Diastereoselective Creation (two chiral centers were generated in product)
A. Enantiodifferentiating Reactions (0 to 2)
B. Diastereodifferentiating Reactions (1 to 2)1. Alkylation of Chiral Enamines2. Alkylation of Chiral Enolates and relater Carbanions3. D-A Cycloadditions4. Micellaneous Reactions
Chem. Rev., 1993, 93, 2037
Current Literature Jingbo Xiao June 5th, 2004
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Intramolecular 1, 3-Chiral transfer Reactions
[2, 3]-Sigmatropic Rearrangement
O R2G
R1 [2,3]-wittig R1 R2
HO G
1 3
Chem. Rev., 1986, 86, 885[3, 3]-Sigmatropic Rearrangement
TBDMSO OBnOH
triethyl orthoacetatepropion acid, 135 oC
TBDMSO OBn1
OEtO
3
Carb. Res., 2000, 328, 37SN2’ Reaction
Ii-Bu
1. t-BuLi2. ZnBr23. CuCN.2LiCl
4.Me
Bu
OCOC6F5
i-Bu
Bu1
3
Org. Lett., 2003, 5, 2111
Current Literature Jingbo Xiao June 5th, 2004
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SN2’ Intramolecular 1, 3-Chiral transfer Reactions
Advantage:
1. Allows the introduction of variable nucleophiles, such as alkyl, alkenyl and aryl groupsinto an existing carbon skeleton.
2. The reactions generally proceed by anti attack of the nucleophile with respect to theleaving group.
Disadvantage:
1. Simultaneous control of the chemo-, regio- and stereo-chemistry is normally difficult.
2. The stereochemistry of the product was determined by the stereochemistry of the startingmaterial.
3. Usually, excess of organometallic reagent is required to push the reaction to complete.
Current Literature Jingbo Xiao June 5th, 2004
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Reagent-directing leaving groups -syn attack
Carbamates as the leaving groups
OCONHPhD
LiCuMe2
D
J. Org. Chem., 1983, 48, 715
Benzothiazole as the leaving group
R1 R2
S S
NLiCuR2
R1 R2
R
J. Org. Chem., 1990, 55, 2295
o-DPPB as the leaving group (DPPB = diphenylphosphanylbenzoate)
O(o-DPPB) 1. eq. CuBr.SMe21.1 eq. MeMgIEt2O, rt, 2h
PPh2
O ODPPB
Adv. Synth. Catal., 2001, 343, 5
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Switchable Directed/Nondirected Leaving Group
ACEI, 2004, Early View Communication
Current Literature Jingbo Xiao June 5th, 2004
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o-DPPB-directed Allylic Substitution
Current Literature Jingbo Xiao June 5th, 2004
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Directed/Nondirected Allylic Substitution
Current Literature Jingbo Xiao June 5th, 2004
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Application of Switchable Directed/Nondirected Substitution in Six-membered-ring System
Current Literature Jingbo Xiao June 5th, 2004
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Conclusion
1. The o-DPPB/o-DPPB oxide system can be used as a switchabledirecting/nondirecting leaving group in a copper-mediated allylicsubstitution reactions.
2. Both enantiomers of the substitution product are readily availablefrom one enantiomer of the substrate.
3. The chemo-, regio- and stereoselectivity are quite good.
4. Large excess of organometallic reagents is NOT necessary.
5. The switchable leaving groups are reusable.